Sealant articles and method of applying sealant

ABSTRACT

A method of making an assembly is disclosed. According to the method, a curable sealant is applied to a metal surface of a first article, and the curable sealant and first article are stored under conditions to maintain the curable sealant in an at least partially uncured state. The method further includes contacting the curable sealant on the first article metal surface with an electrically conductive surface of a second article, and curing the curable sealant.

BACKGROUND

This disclosure is related to sealants, techniques for applyingsealants, and sealant articles.

Sealants are widely used for a variety of applications. For example,sealants can be used to provide a seal between articles againstpenetration of outside materials such as liquids, gases, or solids.Sealants are often used in conjunction with fasteners used to connectarticles together. For example, sealant is often applied to threadedconnectors such as screws or bolts to provide a bond between male andfemale threaded members to inhibit loosening of the threaded connectorthat can be caused by vibration or impact. In some cases, articlescomprising different metal compositions are joined together, such as analuminum structural component and a stainless steel fastener. When thedifferent metal compositions (or a metal composition and a non-metallicelectrically conductive material (e.g., carbon)) have differentelectrode potentials (i.e., one metal is more noble than another metal),the presence of water between the articles can act as an electrolyte andpromote an electrochemical reaction leading to galvanic corrosion. Insuch cases a sealant between the articles of different electrodepotential can be used to help protect against galvanic corrosion byresisting penetration of water between the articles.

Sealants can be applied to articles by various techniques, includingbrush application or various types of injection techniques. In manycases, the sealant is a curable composition that is applied in a liquidor flowable state, followed by curing to a solid or hardened state. Manysealants such as two-component reactive sealants, or sealants having achemical curing reaction initiated by exposure to oxygen or atmosphericmoisture have a limited time period after application before the curereaction is complete. This often necessitates application of the sealantat the time of or shortly before assembly of the article(s) to besealed. Even sealants that undergo a curing reaction whose initiationcan be controlled, e.g., by later application of heat or radiation, canhave a limited time period during which they maintain flowcharacteristics sufficient to allow for compression of the sealantbetween the articles being sealed in order to provide a tight contiguousseal bond.

BRIEF DESCRIPTION

In some embodiments of this disclosure, a method of making an assemblycomprises applying a curable sealant to a metal surface of a firstarticle, and storing the curable sealant and first article underconditions to maintain the curable sealant in an at least partiallyuncured state. The method further comprises contacting the curablesealant on the first article metal surface with an electricallyconductive surface of a second article, and curing the curable sealant.

In some embodiments of the disclosure, an article comprises a metalsurface and a curable sealant on the metal surface, disposed in astorage environment to maintain the curable sealant in an at leastpartially uncured state.

BRIEF DESCRIPTION OF THE DRAWINGS

Subject matter of this disclosure is particularly pointed out anddistinctly claimed in the claims at the conclusion of the specification.The foregoing and other features, and advantages of the presentdisclosure are apparent from the following detailed description taken inconjunction with the accompanying drawings in which:

FIG. 1 is a schematic depiction of a cross-section view of an articlehaving an applied curable sealant thereon;

FIG. 2 is a schematic depiction of a cross-section view of apartially-assembled assembly including the article of FIG. 1;

FIG. 3 is a schematic depiction of a cross-section view of the assemblyof FIG. 2 fully assembled; and

FIG. 4 is a schematic depiction of a cross-section view of anotherassembly.

DETAILED DESCRIPTION

Various types of sealants can be used in accordance with thisdisclosure. Virtually any sealant can be used that has a curingmechanism that can be subjected to storage conditions under which curingof the sealant is inhibited or stopped such that the curable sealant ismaintained in an at least partially uncured state. Examples of sealantsinclude, but are not limited to epoxy sealants, polysulfide sealants,polythioether sealants, polyurethane sealants, polysiloxane sealants(including but not limited to RTV sealant). In some embodiments (e.g.,for aerospace applications), the sealant can be an epoxy sealant or apolysulfide sealant. In some embodiments, the sealant can comprise twoor more reactive components that undergo a cure reaction upon mixingunless subjected to conditions to inhibit or stop the cure reaction.Such sealants are sometimes referred to as two-part sealants ortwo-component sealants. For example two-part epoxy sealants can comprisean epoxy resin that is the reaction product of an epoxide (e.g.,epichlorohydrin) and a diol (e.g., bisphenol A, aliphatic polyol), andan amine or anhydride curing agent that react to form a cured sealant.Polysulfides can utilize mercapto-terminated polysulfide polymers thatundergo curing by oxidation of the terminal mercaptan groups to formextended disulfide bonds, and include oxidizing agents such as manganesedioxide as curing agents to promote the oxidation-based cure reaction.Polythioether sealants can utilize mercaptan-terminated polythioethersthat undergo chain oxide-promoted chain extension curing similar to thepolysulfides. Polyurethanes can utilize a polyol and a low molecularweight polyisocyanate that can spontaneously react to form urethanegroup linkages. Higher molecular weight isocyanate-terminatedprepolymers can be utilized for a cure reaction that utilizes ambientmoisture as a curing agent. RTV silicone utilizes a polysiloxane thathas a cure reaction promoted by a metal catalyst such as dibutyltindilaurate.

As mentioned above, in some embodiments of this disclosure a curablesealant is applied to a metal surface and is stored under conditions tomaintain the curable sealant in an at least partially uncured state.This can be accomplished by various techniques. In some embodiments, thestorage conditions to maintain the curable sealant in an at leastpartially uncured state involve reducing the temperature. Although thedisclosure does not depend on and is not bound by any particular theoryof operation, in some embodiments a reduced temperature can affect themolecular reaction kinetics by reducing available activation energyneeded for the cure reaction, and can also have a cure reactionsuppression effect at the macro level by solidifying (i.e., ‘freezing’)an otherwise fluid mixture of reactants to prevent further intermixingof the reactants. In some embodiments, the article and applied curablesealant are stored at a temperature in a range having a maximum of 0°C., more specifically −25° C., and even more specifically −50° C., and aminimum of −100° C., more specifically −75° C. These range endpoints canbe independently combined to yield various ranges.

In some embodiments, the storage conditions to maintain the sealant inan at least partially uncured state can be conditions that deprive thesealant of a chemical component needed for the cure reaction. In someembodiments, the storage conditions can provide an oxygen-free orreduced oxygen environment to maintain the curable sealant in an atleast partially uncured state. This can be accomplished, for example,with a storage environment under vacuum or with a sealed storageenvironment under a non-oxygen atmosphere such as nitrogen. In someembodiments, the storage conditions can provide a moisture-free orreduced moisture environment to maintain the curable sealant in an atleast partially uncured state. This can be accomplished, for example,with a sealed storage environment under vacuum or with a storageenvironment under a climate controlled de-humidified atmosphereprovided, for example, by a climate control system or desiccant.Combinations of conditions can also be used, such as reduced temperatureand reduced oxygen, reduced temperature and reduced moisture, or reducedmoisture and reduced oxygen.

With reference now to the Figures, FIG. 1 depicts an example of a storedfastener component having applied curable sealant. As shown in FIG. 1, awasher 10 has a bead layer of applied curable sealant 12. Of course,many other types of articles can have applied curable sealant, includingfastener component surfaces (e.g., a washer face, a nut face, a wiringlug face, a bushing face, a bolt or screw head face, a nutplate face, abolt or screw shaft or threads, a spacer, a pin (e.g., cotter pin, dowelpin), a rivet or other surfaces (e.g., structural components to bejoined such as panels, support brackets). The curable sealant 12 can beapplied by various techniques, including but not limited to brushapplication, spray application, roller application, injection nozzledispensing (e.g., dispensing a bead of curable sealant onto thearticle), or printing techniques (e.g., screen printing). The amount andthickness of the layer of applied curable sealant can vary according tothe application. In some embodiments, the curable sealant can be appliedto the entirety of the surface to be sealed. In some embodiments, asexemplified in FIG. 1, the curable sealant can be applied to a portionof the surface to be sealed. In some embodiments, the curable sealantcan be applied to a portion of the surface to be sealed, with theintention of spreading the sealant onto additional portion(s) of thesurface during the assembly process. As further depicted in FIG. 1, thewasher 10 with applied curable sealant 12 is placed into a storageenvironment 14 under conditions to maintain the curable sealant in an atleast partially uncured state.

Although FIG. 1 depicts only a single washer 10, in some embodiments,curable sealant can be applied to multiple articles in a continuousprocess (i.e., assembly line) or a batch process. In some embodiments, aplurality of articles (e.g., fastener components such as washers, nuts,wiring lugs, bushings, bolts, or screws) can be disposed on a support(not shown) such as a plate or tray structure, optionally on componentretaining features such as spindles or recesses matching the shape ofthe component(s), and sealant applied to the batch of the plurality ofarticles. The support carrying the plurality of articles can then beplaced into storage under conditions to maintain the curable sealant inan at least partially cured state, or the articles can be removed fromthe support and placed in the storage conditions. In some embodimentswhere reduced temperature is used, the support carrying the articleswith applied curable sealant can be placed into reduced temperatureconditions to solidify or stabilize the curable sealant, and then thearticles can be removed from the support and returned to cold storage.

With reference now to FIGS. 2 and 3, the washer 10 is removed from thestorage environment 14 and assembled with a bolt 16, a nut 18, and asecond washer 10′ to secure panels 20 and 22 together before the curablesealant can fully cure. FIG. 2 depicts the assembly in apartially-assembled state before tightening of the nut 18 and bolt 16.FIG. 3 depicts the assembly in a fully assembled state after tighteningof the nut 18 and bolt 16. As illustrated in FIG. 3, tightening of thenut 18 and bolt 16 compresses the bead layer of curable sealant 12between the washer 10 and the panels 20/22, displacing a portion of thecurable sealant from the space between the washer 10 and panels 20/22 toform a thin layer of curable sealant 12′. In some embodiments, forexample, where the curable sealant has been solidified (i.e., frozen)from storage under reduced temperature, the curable sealant can beheated or allowed to warm up from exposure to ambient temperatures priorto assembly in order to provide flowability for compression andspreading of the curable sealant. In some embodiments, pressure appliedduring assembly can be sufficient to provide flowability without theneed for warming of the curable sealant. After assembly, having beenremoved from conditions of the storage environment 14 under which thecurable sealant was maintained in at least partially uncured state, thecurable sealant of the assembly of FIG. 3 can complete the curingreaction to form a permanent seal.

FIGS. 2 and 3 depict curable sealant disposed between the washer 10 andthe panels 20/22. In some embodiments, the curable sealant is utilizedto provide a seal between metals of dissimilar nobility (i.e., electrodepotentials) or a metal and an electrically conductive material ofdifferent electrode potentials to resist penetration of moisture to helpprotect against galvanic corrosion. Additionally, in some embodiments,the curable sealant can also provide an electrically non-conductivebarrier between metals of dissimilar nobility (or a metal and anotherelectrically conductive material, e.g., carbon) to further protectagainst galvanic corrosion. For example, the curable sealant can providea seal or a barrier between stainless steel fastener components such aswasher 10 and aluminum panels such as panels 20/22. Of course, thepotential for galvanic corrosion and the benefits of protecting againstit are not limited to combinations of stainless steel and aluminum.Other combinations where curable sealants can be utilized to helpprotection against galvanic corrosion include, but are not limited to,stainless steel and magnesium, titanium and magnesium, aluminum and lowcarbon steel, aluminum and carbon reinforced composites, nickel andaluminum, magnesium and low carbon steel, gold and nickel, or gold andcopper. The placement of the curable sealant in FIGS. 2 and 3 betweenthe washer 10 and the panels 20/22 is of course exemplary in nature, andsealant can be disposed at other locations as is known in the art. Forexample, where the side of panels 20/22 having washer 10 is an exteriorsurface and the opposite side is an interior surface, sealant betweenthe washer 10 and the panels 20/22 may be sufficient to preventpenetration of moisture between the panels 20/22 and any of the fastenercomponents. However, if both sides of the panels 20/22 are exposed tothe elements, sealant can also be placed between the washer 10′ and thepanels 20/22. Sealant can also be disposed at other locations, includingbut not limited to the bolt face 17, the bolt threads 19, the nut face21, or between panels 20 and 22.

Of course, the nut and bolt assembly of FIGS. 2 and 3 is exemplary innature for purposes of illustration, and many other assemblyconfigurations are contemplated. Another illustrative example isdepicted in FIG. 4, which uses the same numbering as FIGS. 2 and 3 todescribe the same or similar components, which are not described infurther detail here. As shown in FIG. 4, a bolt 16, nut 18, and washers10/10′ are used to secure an electrical wiring lug 26 (e.g., anickel-plated copper electrical wiring lug) to a panel or housing 24(e.g., an aluminum housing), with a layer of curable sealant 12′providing a seal between the lug 26 and the panel or housing 24. Suchwiring lugs can be used, for example, to connect electrical componentsto a common electrical plane (e.g., a ground or neutral voltage). Thereare of course many other configurations that can utilize curablesealant, the specific details of which do not require furtherexplanation herein.

While the present disclosure has been described in detail in connectionwith only a limited number of embodiments, it should be readilyunderstood that the present disclosure is not limited to such disclosedembodiments. Rather, the present disclosure can be modified toincorporate any number of variations, alterations, substitutions orequivalent arrangements not heretofore described, but which arecommensurate with the spirit and scope of the present disclosure.Additionally, while various embodiments of the present disclosure havebeen described, it is to be understood that aspects of the presentdisclosure may include only some of the described embodiments.Accordingly, the present disclosure is not to be seen as limited by theforegoing description, but is only limited by the scope of the appendedclaims.

1-15. (canceled)
 16. An article, comprising a metal surface and acurable sealant in a solidified at least partially uncured state on themetal surface, disposed in an external storage environment underconditions to maintain the curable sealant in an at least partiallyuncured state, wherein the curable sealant can be returned to a fluidstate.
 17. The article of claim 16, wherein the external storageenvironment is maintained at a temperature below a curing temperature ofthe curable sealant to maintain the curable sealant in an at leastpartially uncured state.
 18. The article of claim 16, wherein thearticle comprises a fastener component.
 19. The article of claim 18,wherein the metal article surface comprises a washer face, a nut face, awiring lug face, a bushing face, a bolt or screw head face, a nutplateface, a bolt or screw shaft or threads, a spacer, a pin, a rivet, apanel, or a support bracket.
 20. The article of claim 16, wherein thecurable sealant comprises a curable polysulfide sealant, a curable epoxysealant, a curable polyurethane sealant, or a curable silicone sealant.21. The article of claim 16, wherein the external storage environment isan oxygen-free or reduced oxygen environment to maintain the curablesealant in an at least partially uncured state.
 22. The article of claim16, wherein the external storage environment is a moisture-free orreduced moisture environment to maintain the curable sealant in an atleast partially uncured state.
 23. The article of claim 17, wherein theexternal storage environment is maintained at a temperature less than orequal to 0° C.
 24. The article of claim 17, wherein the external storageenvironment is maintained at a temperature less than or equal to −25° C.